Anemia – Macrocytic/Megaloblastic

Anesthesia Implications

Anesthesia Implications

100% O2 – Anemia, in general, is an impairment of the body’s ability to transport O2 to the tissues. Unless contraindicated, give the patient 100% O2 and ensure proper ventilation.

PBRCs (if life threatening) – if this condition has the potential to be life threatening, administer packed red blood cells (PBRCs)

Avoid nitrous oxide – nitrous oxide impairs vitamin B-12 activity, which can further contribute to anemia.

Pathophysiology

This anemia normally manifests as Hemoglobin levels < 10 g/dL, mean RBC volume of 110-140 fL (normal = 90 fL), normal reticulocyte count, increased levels of LDH and bilirubin.

This anemia is characterized by larger-than-normal bone-marrow cells (megaloblastic) and as a result, larger-than-normal (macrocytic) red blood cells are released into circulation.

This condition is due essentially to defects in the sequence in nuclear maturation of cells resulting from: Vitamin deficiencies (eg. Folic acid and vitamin B12), chemotherapeutic agents, and a preleukemic state.

The primary cause is folate and vitamin B12 deficiency – both of which are essential for normal DNA synthesis. Since bone marrow has such a high turnover, it is one of the first to be affected.

Deficiency may be due to: Alcoholism, malnutrition (poor diet), malabsorption, constant exposure to nitrous oxide (eg. recreational use).

B12 deficiency has also been associated with peripheral neuropathy due to degeneration of the lateral and posterior columns of the spinal cord. This manifests as symmetrical paresthesias with loss of proprioceptive and vibratory sensation, especially in the lower extremeties. Other symptoms include unsteady gait, diminished deep tendon reflexes, memory impairment, and depression.

This form of anemia is corrected simply by supplementing folate and B12. If the problem is malabsorption, the route should be parenteral.

References

Hines. Stoelting’s anesthesia and co-existing disease. 7th edition. 2018. 407-436